U.S. patent number 4,651,738 [Application Number 06/762,081] was granted by the patent office on 1987-03-24 for method and device for performing transluminal angioplasty.
This patent grant is currently assigned to Baylor College of Medicine. Invention is credited to Linda L. Demer, Craig J. Hartley, Avanindra Jain, Albert E. Raizner.
United States Patent |
4,651,738 |
Demer , et al. |
March 24, 1987 |
Method and device for performing transluminal angioplasty
Abstract
A novel method and device for performing percutaneous
transluminal angioplasty to treat occlusive artery disease is
disclosed. The method involves simultaneous measurement and display
of the fluid pressure and volume existing within the balloon
catheter as the procedure is performed. Information is produced
which is useful in determining the efficacy of the procedure as it
is performed which obviates the need for arbitrary repeated
inflations. The information is also useful in the subsequent
management of the patient's disease.
Inventors: |
Demer; Linda L. (Houston,
TX), Jain; Avanindra (Houston, TX), Raizner; Albert
E. (Houston, TX), Hartley; Craig J. (Houston, TX) |
Assignee: |
Baylor College of Medicine
(Houston, TX)
|
Family
ID: |
25064060 |
Appl.
No.: |
06/762,081 |
Filed: |
August 2, 1985 |
Current U.S.
Class: |
606/194; 604/920;
606/102 |
Current CPC
Class: |
A61M
25/1018 (20130101); A61M 25/10182 (20131105); A61M
25/10188 (20131105); A61M 25/104 (20130101) |
Current International
Class: |
A61M
25/10 (20060101); A61M 029/02 () |
Field of
Search: |
;128/325,344,348.1,1D,675,DIG.25 ;604/97,98,100 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Olds; Theodore W.
Attorney, Agent or Firm: Fulbright & Jaworski
Claims
What is claimed is:
1. An apparatus for performing, and characterizing the results of,
a transluminal angioplasty procedure comprising:
a balloon catheter means;
a means for filling said balloon catheter means with liquid;
a means for measuring the liquid pressure existing within said
balloon catheter means;
a means for measuring the volume of liquid contained within said
balloon catheter means;
a means for displaying present and past values of the liquid
pressure and volume existing within said balloon catheter
means.
2. An apparatus for performing, and characterizing the results of,
a transluminal angioplasty procedure comprising:
a balloon catheter means;
a liquid supply means adapted to fill said balloon catheter means
with liquid, said liquid supply means being connected to the distal
end of said balloon catheter means and comprising a cylinder means
and a piston means movably mounted in said cylinder means in order
to positively displace liquid from said cylinder means to said
balloon catheter means;
a means for measuring the volume of liquid displaced by said piston
means from said cylinder means into said balloon catheter means
wherein said means comprises a linear displacement transducer which
produces an electrical signal proportional to the distance between
the end of said cylinder means which is connected to the distal end
of said catheter means and the end of said piston means which is in
contact with liquid, said linear displacement transducer means
being physically connected to the cylinder means and the piston
means;
a means for measuring the liquid pressure inside said cylinder
means and said balloon catheter means wherein said means comprises
a pressure transducer which produces an electrical signal
proportional to the liquid pressure and being physically connected
to said liquid between said balloon means and said cylinder
means;
a means for displaying the electrical signals produced by said
linear displacement transducer means and said pressure transducer
means wherein said electrical signals are displayed simultaneously
in analog form on separate axes of the display medium.
3. The apparatus of claim 2 wherein said piston means further
comprises a threaded shaft connected to the end of said piston
means which is not in contact with fluid, wherein said threaded
shaft means is rotatably mounted in an oppositely threaded bore
hole means which is physically connected to said cylinder means,
and wherein said threaded shaft means moves longitudinally through
said bore hole means when said shaft is rotated.
4. The apparatus of claim 3 wherein the threads of said threaded
shaft and bore hole are constructed so finely that manual rotation
of said threaded shaft displaces liquid slowly enough that no
transient pressure waves are produced within the liquid.
5. A method for performing and characterizing the results of a
transluminal angioplasty procedure comprising the steps of:
injecting fluid into said balloon catheter means at a rate slow
enough so as not to produce any transient variations in the
relationship between the volume and the pressure of the fluid
within said balloon catheter means;
independently measuring the pressure and volume existing within
said balloon catheter means and producing electrical signals
proportional to said pressure and volume;
displaying said electrical signals simultaneously in analog form on
separate axes of the display.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention constitutes an improved technique for
performing percutaneous transluminal angioplasty. Angioplasty is a
medical procedure used to treat patients whose arteries have become
occluded due to the disease process call atherosclerosis.
Arteriosclerosis is a general term which refers to any of a group
of diseases in which the lumen of an artery becomes narrowed or
blocked. The most common and important form of arteriosclerosis,
especially in Western societies, is the disease known as
atherosclerosis. In atherosclerosis, there is an accumulation of
lipids in the intimal, or inner, layer of the affected artery. The
resulting intimal thickening restricts the flow of blood so as to
hinder the functioning of, or permanently damage, the organ which
the artery feeds. These accumulations of lipids tend to be
localized and can occur in coronary, cerebral, or peripheral
arteries. They will hereinafter be referred to synonymously as
lesions, plaques, or atheromas.
The lipid accumulation is made up of free lipid and smooth muscle
cells which have proliferated and taken up lipid. As the disease
progresses, the lesion may begin to absorb calcium which causes it
to harden and may also be composed of blood which has clotted in
response to the presence of the atheroma. Although the process of
plaque formation is not completely understood, it is known to be
progressive, and atherosclerotic plaques may vary greatly in their
physical characteristics.
Treatment of atherosclerosis is aimed at alleviating the diminished
blood flow. This can sometimes be done by medical means which cause
the smooth muscles of the arterial walls to relax and thereby
dilate the artery. Other treatment methods are directed toward
physiological compensation for the reduced blood flow. In cases
where the artery is severely occluded, however, there is no
reasonable alternative but to try to re-establish a lumen of proper
diameter. A number of surgical procedures have been developed
toward this end. These include endarterectomy, in which the plaque
is surgically removed, and by-pass grafts, in which a segment of
artery or vein from elsewhere in the body is removed and reattached
in place of the occluded artery. These procedures are major
surgical operations and present a number of disadvantages to a
patient including financial cost, inconvenience, and the risk of
complications associated with any major surgery. Therefore, in the
past several years, methods of re-establishing the patency of an
occluded artery have been developed which are relatively
non-invasive and present less risk to a patient than conventional
surgery. One such method is transluminal angioplasty.
2. Description of the Prior Art
The conventional method of performing transluminal angioplasty uses
a special double lumen catheter. The first, or inner, lumen allows
passage of a guide wire. Concentric with this lumen is a second
lumen which connects to a sausage-shaped segment or balloon at the
distal end of the catheter. The second lumen and balloon are
generally filled with diluted contrast media. Contrast media is
radio-opaque liquid which makes visualization of the catheter
possible by means of X-rays. The procedure first involves selecting
a convenient place to introduce the catheter into the arterial
system of the patient, such as the femoral artery of the leg. Next,
the catheter is guided to the blocked artery. This is done manually
and with the aid of an X-ray monitor. When the catheter is
appropriately positioned, the guide wire is advanced to and past
the point of obstruction. The balloon catheter, which surrounds the
guide wire, is then advanced along with the guide wire until it is
surrounded by the occluding plaque. The balloon, made of material
with high tensile strength and low elasticity, is inflated to a
pressure as high as twelve atmospheres. As the balloon expands it
creates a larger inner diameter within the occluded artery. It is
not known with certainty what physical processes occur within the
occluded artery in response to the balloon inflation, but the usual
method is to inflate the balloon to a certain predetermined
pressure and repeat the inflation an arbitrary number of times. The
balloon is then collapsed and retracted. The site of the
obstruction is then examined angiographically and, if the artery is
still occluded, a decision is made either to repeat the angioplasty
procedure or to resort to some other option.
As aforementioned, the procedure involves inflating the balloon to
a predetermined pressure. Although the operator may observe the
size of the balloon during the inflation by means of the X-ray
monitor, unless the pressure is measured, the bursting pressure of
the balloon may be exceeded causing rupture. Therefore,
practitioners have realized the need for continuous monitoring of
the fluid pressure within the balloon. As it is conventional to
inject fluid into the balloon with a syringe, the most obvious
method is to interpose a T-fitting between the delivery end of the
syringe and the balloon catheter. A standard pressure transducer
can then be connected to the T-fitting and the fluid pressure
within measured. U.S. Pat. No. 4,370,982 discloses a method for
measuring fluid pressure without the transmitter coming in contact
with the working medium. The '982 patent also discloses an
injection device which uses a threaded member which when rotated
produces translational motion of the syringe plunger. The
relatively slow inflation is supposed to reduce further the risk of
balloon rupture.
Another relevant patent is U.S. Pat. No. 4,446,867 which discloses
a method and apparatus for generating pulses of pressure within the
balloon catheter. As discussed above, some atheromas become hard
due to calcification and therefore resist dilation by the balloon.
The '867 patent represents an attempt to deal with this problem by
inflating the balloon so rapidly that the plaque is broken.
Although the specification of the '867 patent recites that pieces
of broken plaque will be removed by normal cardiovascular
processes, it seems obvious that such fragments may flow downstream
and become lodged in a smaller artery, thereby completely blocking
blood flow. As pieces of plaque may break off during conventional
angioplasty procedures, even without using the pulsed pressure
method of the '867 patent, it is important to know when this has
occurred so that remedial steps may be taken.
SUMMARY OF THE INVENTION
One major problem with transluminal angioplasty is that there has
heretofore been no means of evaluating the efficacy of the
procedure contemporaneous with the performing of it. This has
resulted in the establishment of arbitrary performance protocols
whereby the balloon is inflated repeatedly an arbitrary number of
times. Because the pressures involved are necessarily high, each
subsequent inflation presents a risk of balloon rupture. It would
be advantageous if the operator had some means of judging when the
procedure had succeeded or failed and whether a subsequent
inflation could be expected to succeed. As atherosclerotic plaques
vary greatly in their physical characteristics, what is needed is a
means of monitoring the underlying physical events occurring within
the occluded artery as the balloon in inflated. Not only would this
be helpful during the performance of the procedure itself, but it
would make possible a more accurate prognosis of the course of the
patient's disease and aid in evaluating other treatment
options.
The present invention accomplishes this objective by providing for
the simultaneous monitoring of both pressure and volume changes
occurring within the balloon as the angioplasty procedure is
performed. By the use of basic physical principles, the
pressure-volume curves thus generated can be correlated with the
physical changes taking place within the occluded artery.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts the pattern of a typical pressure-volume curve
generated when an expanding balloon compacts or compresses the
plaque material against the artery wall.
FIG. 2 depicts the pattern of a typical pressure-volume curve
generated when an expanding balloon stretches the artery wall
itself.
FIG. 3 depicts the pattern of a typical pressure-volume curve
generated when an expanding balloon causes fractures in a plaque
composed of relatively rigid material.
FIG. 4 is a drawing of the device used to perform the angioplasty
procedure in accordance with the present invention.
DESCRIPTION OF THE INVENTION
The best mode and preferred embodiment of the invention is
illustrated in FIG. 4. The proximal end of the balloon catheter 1
is attached to the inflation syringe 3. The syringe is of standard
type but modified for reasons which will be apparent below. A
plunger 10 moves through the barrel of the syringe 3 displacing
liquid, such as diluted contrast media, into the balloon catheter
1. The plunger shaft 7 is finely threaded all along its length so
that when turned, the shaft moves longitudinally through an
oppositely threaded annular member 8. The annular member 8 is
attached to the syringe 3. In this way, slow and even displacement
of liquid into the balloon catheter is produced by rotating the
shaft 7. The more fine the threads, of course, the slower will be
the fluid displacement. A hand crank 4 has been added to facilitate
the balloon inflation process.
Interposed between the balloon catheter 1 and inflation syringe 3
is an electronic pressure transducer 2 of conventional type. An
electronic signal proportional to the fluid pressure existing
within the catheter is then fed to an oscilloscope 9 for real-time
display. Any type of electronic recording device could also be
used. A linear displacement transducer 6, which produces an
electronic signal proportional to its length at any given time also
feeds into the oscilloscope 9. The ends of the linear displacement
transducer 6 are connected by means of coupling bars 5a and 5b to
the plunger shaft 7 and inflation syringe 3 respectively. In this
way the signal produced by the linear displacement transducer 6 is
proportional to the volume of fluid displaced from the syringe 3
and hence residing in the balloon catheter 1. Thus, there are two
electronic signals fed to the oscilloscope 9 which represent the
volume and pressure of the fluid contained by the balloon at any
given time. By displaying the pressure and volume inputs
simultaneously a curve is generated by the oscilloscope wherein one
axis corresponds to pressure and the other axis corresponds to
volume. The information contained in this curve enables one to draw
certain conclusions regarding the physical process taking place
during the dilation process as will now be explained.
FIGS. 1-3 depict expansion curves generated by dilating models of
arterial lesions with three different types of behavior.
Superimposed on all three figures is the expansion curve 10 of the
balloon expanded by itself. This represents the compliance of the
balloon alone and will be used as the reference curve.
Referring first to FIG. 1, expansion curve 12 shows that as the
pressure is raised initially, there is little change in the volume
of the balloon as compared with the reference curve 10. This
indicates that the atherosclerotic plaque which surrounds the
balloon is preventing the balloon from expanding. As the pressure
is increased further, however, the pressure within the balloon
becomes great enough to overcome the resistance of the plaque
material. At this point the occluded artery begins to dilate as the
balloon expands. It is not clear whether the plaque material is
actually compressed so as to occupy less volume or is deformed so
as to be redistributed along the length of the artery, but what is
important is that the expansion takes place at relatively constant
pressure. At any given point along the curve, the pressure of the
fluid within the balloon is exactly balanced by the pressure
exerted by the surrounding plaque. A region of constant pressure,
or isobaric, expansion indicates that the plaque material is
exerting the same force irrespective of the extent of the plaque's
deformation. The theory of the properties of materials would
predict that the stress exerted on the plaque had exceeded the
yield point of the plaque material. This would mean that the plaque
material is being deformed plastically rather than elastically.
This is consistent with a young or at least still malleable
atheroma which can be expected to retain the deformation produced
by the expanded balloon. Thus, when an expansion curve like that of
FIG. 1 is obtained, the operator may infer that the angioplasty
procedure has been relatively successful and no further inflation
cycles are necessary, especially if a repeat inflation yields a
curve superimposed on curve 10. Furthermore, the knowledge that the
atheroma responded to the procedure in this way is useful in the
subsequent management of the patient's atherosclerotic disease.
Next, in FIG. 2, is an expansion curve 14 which indicates that as
the balloon expands against the occluded artery, the artery exerts
increasing force against the balloon. This would lead one to
conclude that the occluded artery is acting like a spring and
storing the work of expansion only to return to its former occluded
shape when the balloon is deflated. This has been found
experimentally to be the case although with repeated inflations the
curve sometimes moves closer to the reference curve indicating that
the artery is becoming more compliant. Unlike the case in FIG. 1,
the atheroma in this example has probably been deformed very little
by the expanding balloon. Since plaque is known not to be composed
of elastic, or energy storing, material the likely source of the
elasticity is the medial layer of the arterial wall itself. In any
case, an expansion curve like that in FIG. 2 indicates a less
desirable result for the patient than that in the first example
above. The increased compliance of the arterial wall following
repeated inflations may also indicate plastic changes such as
thinning and microscopic tearing, such that it would be hazardous
to try another inflation cycle.
Finally, FIG. 3 shows an expansion curve 16 exhibiting sharp drops
in pressure as the balloon expands. A sudden decrease in the
pressure exerted against the balloon by the occluded artery can
only mean that a stress relieving fracture of some kind has
occurred. One can then infer that the plaque was hard and brittle,
presumably due to calcification, and was fractured by the expanding
balloon. Not only does this indicate that angioplasty is not likely
to be successful in dilating the artery, but remedial steps may
need to be taken to prevent the plaque fragments from separating
from the rest of the plaque causing complications at some point
downstream. One such remedial step might be to inflate the balloon
a second time, although at a lower pressure, in order to "tack" the
plaque fragments down and prevent their dislodgment. Anticoagulant
therapy may also be indicated.
In generating the expansion curves discussed above, the particular
instrumentation used must be able to respond to the extremely small
changes in volume involved when the balloon expands as well as
pressures reaching twelve atmospheres. The inflation syringe
described in the preferred embodiment was also constructed with a
shaft possessing screw-type threads fine enough so that many
rotations are necessary to move the shaft through the oppositely
threaded annular member. A slow and even displacement of fluid into
the balloon is necessary to avoid introducing artifacts into the
pressure signal and obscuring the information contained therein.
That is, a properly constructed expansion curve only contains
pressure values which have been obtained after any transient
pressure waves in the fluid have died out.
It should be understood that the embodiment disclosed hereinabove
is not meant to limit the invention in any manner. On the contrary,
it is intended to cover all modifications, alternatives, and
equivalents as may be included within the spirit and scope of the
invention as defined by the following claims.
* * * * *